Ana can be highly emotional and empathetic. She craves attention, although she often hides behind others. And she can be a complete bitch.

''Get back on track, you ignorant f---.

Lose it, Chub. Lose it. Now.

Cut and starve and drink.

This is who you are now.''

- Ana

''Ana'' is not a real person but an identity, adopted as self, friend and foe, the embodiment of anorexia. Her speech is the self-talk and self-hate that typifies a condition that is all about internalising how you look - or think you look - on the outside, and clinging to the conviction that salvation lies in getting ever thinner.

Ana (short for ''pro ana'' - pro anorexia) and her lesser known sibling Mia (or ''pro mia'' - pro bulimia) are the subjects of countless posts on social media and dedicated websites, blogs and forums. In 2008, the Eating Disorders Foundation of NSW (now Butterfly Foundation) estimated there were more than a million such sites.

Pro ana is dedicated to encouraging and supporting those who identify with the community. There are tips on grim topics such as how to make yourself vomit (known as ''purging'', one involves dental floss and a lifesaver). There are images of skinny models, celebrities and users' own ''selfies'' (called ''thinspiration'' or ''thinspo''). And there are heartfelt posts describing good days and bad, and real-time messaging from Ana ''buddies''.

Those who participate in the subculture appear to be overwhelmingly teenage girls and young women - although online it is impossible to be sure - using handles such as ''anything2bethin'' and ''beautifulbones''. The tone of the sites combines the language of support groups and their cycles of hope, commitment, breach, despair and recommitment, with a slightly childish emo folksiness (poetry in scratchy fonts, artwork of waifs wearing knee socks) and a rather more grown-up pride in their perversity.

Coffee and smokes

and cold Diet Cokes,

That's what pretty girls are made of.

Its manifest catharsis is profoundly shocking.

Emma, 21, has struggled with an eating disorder for five years (her surname has been omitted to protect her privacy). She has starved herself (''restricted'') for up to eight days at a time (''No food whatsoever and zero-calorie drinks. And I end up a mess after it. I do really want to stop it.''). She has seen a range of psychologists, counsellors, dietitians and support groups to help her break a cycle of fasting and bingeing, and deal with her related anxiety and self-harming.

While still at school, Emma told her friends about her messed up behaviours, but, after that one tearful night, they were never mentioned again. She feels lonely and isolated. She has to force herself to leave the house other than to go to work, and she avoids talking on the phone.

Having always done a lot of research online, Emma stumbled into the pro ana community at the beginning of the year.

''It's actually nice to read,'' she says. ''It makes me feel like I'm not alone, like other people are going through these things and people understand.''

Intelligent and articulate, Emma is ambivalent about the subculture. ''I go through stages where I think pro ana is a fantastic idea, and I get right into it, I read about it and I look for buddies. Then all of a sudden I'll binge and then I'll be, like, obviously, restricting isn't a realistic plan for me.''

Her life is dominated by the disorder, she says, every day an exhausting struggle with whether she will try to eat normally or fast.

''Even if I try and eat normally, because I've developed a habit of bingeing, I'll still binge. If [that] happens many times, I feel like I can't do it any more, I need a break. And so I'll go back to restricting. Pro ana is sort of there for when I can't fight any more,'' she says.

Yet she is clear-eyed about pro ana's hazards. ''It does scare me too,'' she says. ''I [was] talking to someone on there once … and she was 13 or 14, and that just breaks my heart. I feel like saying stop, don't get into this mess, get out of it while you've got the chance.''

Most eating disorder specialists and support groups are unequivocal about the sites' dangers.

''I absolutely hate them,'' says Christine Morgan, the chief executive of the Butterfly Foundation, the national support group for sufferers and carers. Those with long-term eating disorders don't want to get well, she says. ''That's one of the most horrific aspects of the illness.

''The sites say that [people] have chosen this as a lifestyle. We know that's not true, that it's a very serious psychiatric illness. Then they encourage them to remain true to behaviours that are doing them harm. I can't see anything positive in that from any perspective.''

Two million people in Australia will suffer from an eating disorder in their lifetime, the foundation estimates. Disorders last an average of 15 years, and about 20 per cent of sufferers never recover. It estimates the health costs at about $100 million last year, with an effect on national productivity of about $15.1 billion.

Physical damage can include anaemia, osteoporosis, an increased risk of infertility and kidney failure. The foundation estimates last year about 1828 sufferers died. Beyond the mortality rate and physical impairment, experts in eating disorders argue the behaviours must be understood as a mental illness because of the huge distress they cause.

Chairwoman of mental health at the University of Western Sydney, Professor Phillippa Hay, likens eating disorders to depression. ''In the course of human experience, it will be normal to feel low in the same way as someone with depression feels low. But for someone with a mental illness, [it] becomes overwhelming and prevents them from living full and happy lives and relating to other people. It's the disability from the behaviour and emotion that constitutes an illness.''

Many sufferers are unable to work, have a relationship or live independently.

Internationally, there has been momentum in several countries to ban or attach warnings to pro ana sites, including France, Britain and the Netherlands. In Australia, the federal Labor MP, Anna Burke, called for legislation banning pro ana sites in 2008.

But how much harm do they cause? Emma says pro ana's virtual solidarity is something she hasn't been able to find in real-world support groups: She likes not being seen, and the ability to have text conversations when she needs them.

She prefers their support to that of professionals she has consulted. ''I've never liked the idea of paying to have someone to talk to. It feels like they're only doing it because they have to.'' Pro ana, on balance, has been more good than bad, she says.

Last year, a ground-breaking study of the personal experience of pro ana bloggers was published in the journal Health Communications. It found bloggers experienced positive effects of self-expression, catharsis and social support in coping with a stigmatised disease. They also experienced negative consequences: fear of disclosure and of encouraging disorders.

Researchers Daphna Yeshua-Katz and Nicole Martins concluded that, in light of the poor results of conventional treatments for eating disorders - those treated for anorexia have less than 50 per cent chance of recovering within 10 years - further investigation of the prevailing treatment protocols were warranted.

''Instead, the young [pro ana] women themselves are blamed for sabotaging their own recovery,'' they argue. ''Our results suggest … the moral panic about the websites might not be appropriate.''

Parallels with pro ana can be found in the fat acceptance movement, which aims to change social and medical prejudices about those with large bodies. Both are trying to break down stereotypes that looking a certain way makes people bad, moral or aesthetic failures.

Like Gay Rights, Women's Lib or Deaf Culture, these are arguably all identity movements that aim to recast as diversity those traits condemned as disease or disability and used as the basis for discrimination. If fat acceptance rightly seeks to de-stigmatise the large bodied, why couldn't the same be true of pro ana? Because unlike obesity, the experts say, anorexia is a mental illness. The categorisations of mental illnesses, however, are not like the laws of physics. ''Disordered'' behaviours can move in and out of the medical/psychological spectrum over time: homosexuality, notoriously, was removed from the Diagnostic and Statistical Manual of Mental Disorders in 1986.

Ethicist Stacy Carter, who works at the University of Sydney's school of public health, says if anorexic behaviour has its roots in damaging experiences, it is legitimate to question ''whether that person is in a position to make good judgments about how to live a flourishing life.

''If the very nature of being anorexic is the state of being constantly miserable, then it would make more sense to do whatever you could to [intervene],'' she says.

But if young women are attracted to pro ana websites, that immediately suggests they need a community they can identify with, she says. ''So shouting at them about it being bad to be anorexic and trying to shut down the sites seems to miss the very purpose of their engagement with the sites in the first place. Maybe a better way to think about it is, how can we provide that?''

Hay says a ''counter culture'' of therapeutic applications that seek to do just that are emerging, including chat rooms and ''therapies that can be delivered ethically over the internet''.

But it is not just the technology that enables pro ana. It is also its uncensored, unsupervised nature.

In the weeks after interviewing Emma, I regularly check her activity on her favoured pro ana site. She's back there most days but hasn't posted a comment asking for, or offering, support since I first contacted her via the site.

I feel my anxiety about her is well intentioned. But I suspect she feels she's being watched.

For help and support call 1800 334 673 or email support@ thebutterflyfoundation.org.au